B. a country is harboring terrorists responsible for attacks on the U.S.
Explanation:
The Powell Doctrine is a term that is used for a policy that is primarily focused on defense of the country and preventing attacks on the country, usually by using military force. In order for a military attack to be approved though numerous things have to be taken in consideration, examined, and answered.
From the presented scenarios, the Powell Doctrine would enable the U.S. the intervene in a country is harboring terrorists responsible for attacks on the U.S. Such examples in the past few decades have been the war in Afghanistan because of Al-Qaeda, and the war in Iraq, also because of Al-Qaeda. A military intervention also occurred in Iraq and the neighboring Syria because of the rise of the terrorist organization ISIS among other reasons.
Irish monasteries became famous for their learning and many students came to study in them from other parts of Europe. Irish monks also spread Christianity across Europe.
